Association of gestational anemia with pregnancy conditions and outcomes: A nested case-control study

Table 1 General characteristics of the pregnant women who participated in this study

Characteristics	n = 3172	Percentage
Ethnicity
Han	3082	97.2
Others	90	2.8
Age in yr
< 20	106	3.3
20-25	318	10.0
25-30	1473	46.4
30-35	908	28.6
35-40	301	9.5
≥40	66	2.1
Educational level
Primary school or lower	19	0.6
Junior middle school	493	15.5
High school	655	20.7
College	1784	56.2
Master’s degree	206	6.5
Doctoral degree	15	0.5
Number of permanent residents in family
1	37	1.2
2	951	30.0
3	706	22.3
4	725	22.9
5	550	17.3
6	119	3.8
≥ 7	68	2.1
Unknown	16	0.5
Geographic distribution
East	694	21.9
Middle	498	15.7
West	394	12.4
South	572	18.0
North	1014	32.0
Place of residence
Urban registration	1346	42.4
Rural registration	1826	57.6
Clinical characteristics
Anemia	443	14.0
Premature rupture of membrane	398	12.6
Gestational diabetes mellitus	372	11.7
Gestational hypertension	84	2.7
Occupation
Unemployed	929	29.3
Administration	319	10.1
Professional	504	15.9
Office clerk	312	9.8
Business services industry	607	19.1
Agricultural industry	64	2.0
Others	437	13.8
Personal annual income (Yuan, thousands)
0	207	6.5
≤ 10	214	6.8
≤ 20	308	9.7
≤ 30	486	15.3
≤ 40	362	11.4
≤ 50	571	18.0
≤ 60	281	8.9
≤ 70	82	2.6
≤ 80	145	4.6
≤ 90	18	0.6
≤ 100	295	9.3
≤ 150	94	3.0
> 150	73	2.3
Unknown	36	1.1
Family annual income, in Yuan, thousands
0	25	0.8
≤ 20	115	3.6
≤ 40	206	6.5
≤ 60	451	14.2
≤ 80	317	10.0
≤ 100	661	20.8
≤ 120	144	4.5
≤ 140	52	1.6
≤ 160	302	9.5
≤ 180	68	2.1
≤ 200	404	12.7
≤ 250	88	2.8
≤ 300	159	5.0
> 300	136	4.3
Unknown	44	1.4
Body mass index in kg/m²
< 18.5	420	13.2
18.5-24.0	2062	65.0
24.0-28.0	556	17.5
≥ 28.0	134	4.2
Gestational weight gain in kg
< 2.5	46	1.5
2.5-5.0	25	0.8
5.0-7.5	169	5.3
7.5-10.0	202	6.4
10.0-12.5	717	22.6
12.5-15.0	479	15.1
15.0-17.5	760	24.0
17.5-20.0	286	9.0
20.0-22.5	302	9.5
22.5-25.0	67	2.1
25.0-27.5	83	2.6
≥ 27.5	36	1.1

Table 2 Results of univariable logistic regression analysis

Characteristics	P value	OR	95%CI of OR
			Lower	Upper
East region	< 0.01
Middle region	< 0.01	0.6	0.47	0.76
West region	< 0.01	0.66	0.51	0.85
North region	< 0.01	5.95	4.33	8.18
< 20 yr	0.01
20-25 yr	< 0.01	5.93	2.1	16.74
25-30 yr	0.01	4.12	1.5	11.32
30-35 yr	0.01	3.96	1.43	10.94
35-40 yr	0.01	4.48	1.57	12.78
> 40 yr	0.09	3.03	0.85	10.77
Preterm	0.03
Full-term birth	0.01	0.59	0.39	0.88
Rural registration	< 0.01	1.58	1.28	1.95
PROM	< 0.01	1.61	1.23	2.11
BMI classification	0.41
Gestational weight gain classification	0.57
Primary school or lower	< 0.01
Junior middle school	0.98	1.01	0.33	3.12
High school	0.46	0.65	0.21	2.01
College	0.21	0.49	0.16	1.49
Master’s degree	0.31	0.54	0.17	1.76
Doctoral degree	0.42	1.87	0.4	8.74
Unemployed	0.02
Administration	0.2	0.79	0.54	1.14
Professionals	0.1	0.77	0.56	1.05
Office clerk	0.07	0.7	0.48	1.03
Business services industry	0.06	0.75	0.56	1.01
Agricultural industry	0.03	1.88	1.05	3.36
Others	0.09	0.75	0.54	1.04
Personal annual income	< 0.01
Family annual income	< 0.01

BMI: Body mass index; CI: Confidence interval; OR: Odds ratio; PROM: Premature rupture of membranes.

Table 3 Results of multivariable logistic regression analysis

Characteristics	P value	OR	95%CI of OR
			Lower limit	Upper limit
East region	< 0.001
Middle region	< 0.001	0.428	0.331	0.553
West region	< 0.001	0.406	0.309	0.533
North region	< 0.001	7.169	5.139	10.003
< 20 yr	0.07
20-25 yr	0.077	2.635	0.900	7.711
25-30 yr	0.245	1.856	0.654	5.269
30-35 yr	0.367	1.623	0.567	4.646
35-40 yr	0.399	1.596	0.538	4.738
> 40 yr	0.961	0.968	0.259	3.617
Full-term birth	0.002	0.491	0.316	0.763
PROM	0.022	1.404	1.051	1.876

CI: Confidence interval; OR: Odds ratio; PROM: Premature rupture of membranes.